Many vehicles, such as, for example, automobiles, on-highway trucks, or off-highway trucks often include a four stroke internal combustion engine that provides power for the vehicle. Four stroke internal combustion engines typically undergo an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. To control the flow of gasses into and out of an engine's combustion chamber during normal operation, internal combustion engines typically include a group of valves. Under normal operating conditions, for example, when the engine is producing positive work, the intake and exhaust valves are typically closed during both the compression stroke and the expansion stroke. The intake valve is usually opened during the intake stroke to allow air to be drawn into the combustion chamber, and the exhaust valve is usually opened during the exhaust stroke to allow exhaust gas to be expelled from the combustion chamber. In addition to controlling the flow of gasses with respect to combustion, the flow of gasses may also be controlled to provide a retarding force against an engine piston. A retarder, also known as a compression release brake, is well known in the art for absorbing energy and reducing vehicle speed without the need to activate a service brake.
Retarders are routinely used on the open highway as well as in urban areas. Due to the noise generated by the retarder during compression release braking, many jurisdictions have instituted noise level restrictions, particularly in residential areas. Traditional retarders typically produce noise levels that exceed the maximum noise levels allowable by law. For this reason, vehicle operators are routinely prohibited from operating traditional retarders. As a result, the operator must rely on the service brake to slow the vehicle in cases where the retarder could otherwise be used to avoid wear and/or overheating of the service brake.
One way to reduce the noise generated by a retarding stroke is discussed in U.S. Pat. No. 5,357,926 (the '926 patent) issued to Haoran Hu. The '926 patent discloses a retarder which can be switched, whenever desired, between a normal mode of operation and a quiet mode of operation. In the normal mode, the retarder is set so that the exhaust valves are opened relatively close to top-dead-center. For example, in the normal mode the exhaust valve in an engine cylinder may be opened at an engine crank angle of approximately twenty degrees to thirty degrees prior to top-dead-center. By opening, or “blowing down” the valve near top-dead-center after the engine has significantly compressed the air, the normal mode provides relatively more braking power and also creates relatively more noise. In the quiet mode, the exhaust valve may be opened, or blown down, at an engine crank angle of sixty degrees to seventy degrees prior to top-dead-center. By opening the valve at this time, noise generated during the retarding stroke is reduced compared to the normal mode.
Although the '926 patent provides a retarder capable of operating in a quiet mode, certain disadvantages persist. For example, in quiet mode, the retarder of the '926 patent may still provide the high intensity noise associated with the blow down event.
The disclosed retarding system is directed to overcoming one or more of the problems set forth above.